Evolution
in press
Sequence evolution of the sperm ligand zonadhesin correlates
negatively with body weight dimorphism in primates
Herlyn H, Zischler H
Abstract
Sexual selection has repeatedly been shown to be the probable driving force behind the
positive Darwinian evolution of genes affecting male reproductive success. Here we
compare the sequence evolution of the sperm ligand zonadhesin with body mass
dimorphism in primates. In contrast to previous related studies, the present approach
takes into account not only catarrhine primates, but also platyrrhines and lemurs. In
detail, we analyse the sequence evolution of concatenated zonadhesin fragments (555
bp) of four Lemuroidea, five Platyrrhini, and seven Catarrhini, using the rate ratio of
nonsynonymous to synonymous substitutions (dn/ds = ω). Unexpectedly, subsequent
regression analyses between ω estimates for the terminal branches of a primate
phylogeny and residual male body mass reveal that sequence evolution of zonadhesin
decreases with increasing sexual dimorphism in body weight. Mapping published mating
system classifications onto these results illustrates that unimale breeding species show a
tendency for rather slow sequence evolution of zonadhesin and comparably pronounced
sexual dimorphism in body weight. Female choice and sperm competition can be
assumed to drive the evolution of zonadhesin. We speculate that the level of sperm
competition is lower in more sexually dimorphic primates because males of these species
monopolize access to fertile females more successfully. Thus, variation in sperm
competition may be driving the observed negative correlation of sequence evolution and
sexual dimorphism in body weight.